Encapsulation, an old art, is playing an ever increasing role in the food and in related industries. Many patents and other publications deal with the encapsulation of ingredients used in foods. In modern food processing it is essential that products have long shelf life and have excellent stability. Encapsulation plays a major role in satisfying these requirements.
For example, encapsulation makes it possible to stabilize and to protect essential oils from deterioration and loss during storage. Encapsulation may protect the potency and greatly increase the shelf life of oxidation-sensitive materials such as Vitamin A. Another important application relates to the stabilization of metallic compounds such as ferrous sulfate as well as copper salts and other minerals which may act as pro-oxidants.
The major encapsulation process in use today involves dissolving a gum or a modified starch in water, adding, for example, an essential oil with suitable agitation to produce an emulsion, and spray drying. In other procedures a solution of a protein such as gelatin serves as an emulsifying agent. A gel is formed and this is carefully dried and ground. Other techniques use sugar melts as protective encoating agents. Many applications use starches or flours. These are gelatinized followed by emulsification and spray drying. Fats have also been used as protective coatings.
Applicants' present invention constitutes a new approach to encapsulation. The method of the invention, using an extrusion step, is extremely simple and has many advantages over prior art processes.
In the last decade hundreds of patents have issued which deal with the structuring of vegetable proteins. The efforts in this area have been extensive. Extrusion has been a favorite technique for making many food products such as breakfast foods, snacks and breadings.
In such prior art extrusion processes, the products produced are friable and essentially ready to eat. All are expanded or "puffed", similar to a product such as puffed rice. In more recent years textured vegetable protein products have been developed. In Atkinson, U.S. Pat. No. 3,488,770, soy flour, moistened with about 30% by weight of water, is passed through an extruder in which heat and applied pressure convert the moist mass to a molten state or melt. This material is then exploded into the atmosphere to produce what is known as textured vegetable protein (TVP). The product is porous and friable, and is intended to simulate or replace meat.
In searching for new forms of vegetable protein which could be used for the food supply, Sair & Quass U.S. Pat. No. 3,968,268 devised an extrusion process for forming a dense transluscent, glassy protein. This product was quite different from the products produced by Atkinson, and different from the extruded breakfast cereals, snacks, and breadings. The glassy protein was hard and vitreous and not edible in this form. Additional cooking or hydration was needed as in the case of rice, wheat or other grains. The protein glass of Sair & Quass was produced by applying heat and pressure to a moist protein mass and extruding under conditions which prevent puffing.
In prior art encapsulation processes, as commercially practiced, the ratio of water to encapsulating agent has been, for example, 2 to 1, to 5 to 1. Sufficient water is added to produce a solution, followed by suitable emulsification. In reviewing the technology used in developing simulated meat products such as textured vegetable protein the inventors herein queried whether there might not be a completely new encapsulation procedure constituting a major advance over the prior art. Specifically, if one could utilize the extrusion process to produce a molten, unpuffed glass or melt of a polymeric material to effect encapsulation, the development would have the following advantages:
1. Extrusion is a continuous process, and it is simple. PA1 2. During extrusion one could use minimal water, whereby drying conditions would be greatly simplified. Spray driers could be eliminated. PA1 3. The finished product could be shaped to any desired form. One would not be limited to fine (spray-dried) particles. PA1 4. Extrusion would result in a microencapsulation within a matrix of controlled solubility. Release of the encapsulated agent would be gradual, dependent on hydration of the matrix.
Still other advantages become evident.
Glass formation is not unique to proteins. Mercier and Feillet in Cereal Chemistry, Vol. 52, page 283 (1975) describe glasses formed from cereal-like materials.
It was known that certain polymer films such as polyethylene may serve to protect hygroscopic materials but afford very little protection for the essential oils of flavorings. It was also known that other polymer films such as cellophane are suitable to protect essential oils. The essence of the present invention is the surprising discovery that protein and cereal polymer matrices behave like cellophane, providing excellent protection of encased agents, including essential oils, in an encapsulation process. It was also found that, upon hydration of the polymer matrix, the encased agent was gradually released in a highly effective form.
In the conventional prior art extrusion procedures being used to produce cereals, snacks, breadings and textured vegetable proteins, it is known that if a flavoring is added to the material prior to extrusion much of the flavoring agent is lost during the puffing expansion. Accordingly, the accepted method has been to add the flavor oil or other flavoring agent only after extrusion. An example is a product sold under the name BACOS. The product consists of small chunks of vegetable protein made by the process described for producing textured vegetable protein. The small porous chunks of material are then treated with vegetable oil to which the selected flavor agent has been added. The snack industry has continued its search for flavoring materials that can be added prior to the extrusion step, but with no success. The extruded polymer glasses of the present invention, in which expansion or puffing is deliberately prevented, provide a novel and unobvious encapsulating medium to produce valuable concentrates of flavors and other agents.
Typical of prior art methods is that described in Katzen U.S. Pat. No. 3,786,123 which teaches an extrusion process for stabilizing and preserving nutrients and other ingestible agents. But the Katzen process is totally unsuited to produce the flavor concentrates of the present invention, because Katzen resorts to explosion puffing, to form a porous product. In controlled tests, it has been found that when 4% of oil of sage is incorporated in a mixture and then extruded following the Katzen teachings, half of the essential oil is lost. In contrast, the process of the present invention, produces an unpuffed, vitreous glass, over 90% of the essential oil being retained in the final product. Katzen teaches only an expanded, porous product. He suggests no dense glasseous extrudate. The Katzen process, for producing a porous product, cannot be used to encapsulate an agent having volatile constituents.
In accordance with the practice of the present invention it has been found that for some applications one type of extrudate glass is superior to another as the matrix. For example, it has been found that certain flavor oils such as mustard flavor oil (containing allylisothiocyanate) undergo objectionable reactions with functional groups of proteinaceous materials to yield final products which do not have the odor and flavor of mustard. On the other hand when a cereal base material is used as the glasseous matrix for the allylisothiocyanate, the final concentrate has true mustard flavor. In the encapsulation of lemon flavor for use with tea, it has been found that the citric acid in the lemon flavor agent reacts with alkaline functional groups of a proteinaceous glass so that the citric acid is not released when the flavor concentrate is added to hot water. In contrast, when a cereal glass encapsulating matrix is used, no functional groups interfere, and the citric acid is immediately released to the tea along with the other lemon flavor elements.
Still other considerations may dictate the selection of special encapsulating agents in particular applications of the present invention. When more rapid solubilization and release are required, a cereal glass is used in preference to protein. When still more rapid solubilization is desired, a gum glass or a modified starch glass may be used as the extrudate matrix.
In the encapsulation of iron for incorporation in cereal products, the aim of industry has been to add the iron prior to extruding. Several approaches to dealing with the problem have been unsuccessful. For example, when hard fats are used to encase minerals such as iron, the high cereal processing temperatures cause the fat to melt and to liberate the mineral prematurely. Some proteinaceous encapsulating materials dissolve during the processing and release the minerals. In accordance with the practice of the present invention, the use of wheat gluten as an encapsulating material effectively solves the problem. Wheat gluten is quite insoluble in water. When iron is encapsulated in a water-insoluble wheat gluten glass, in combination with an additional water-proofing agent such as zinc stearate, in accordance with the present invention, the ground product withstands processing intact, the iron being retained within the fused, water-insoluble protein matrix.
Depending upon the agent to be encased, concentrations of up to about 40% or more may be effectively encapsulated in the polymeric matrix. The food supplement concentrations of the invention may be added to food products in concentration of up to about 15%, or higher.